The objective of this research proposal is to determine the biological feasibility of using hyperthermia as a treatment modality for brain tumors. Thermal dosimetry studies will be carried out in animals using both uniform ultrasound fields and a phased array microwave applicator. Measurement of the ultrasonic and thermal properties of skull and brain tissues, in vitro and in vivo, will be performed as a function of ultrasonic frequency and temperature. The threshold levels for thermal damage to the central nervous system will be studied in detail. The effects of hyperthermia in combination with radiotherapy on normal central nervous system tissue will be studied in a series of chronic animals. Out of these studies a thermal dosimetry treatment plan format will evolve. Dogs with spontaneous brain tumors will be treated according to the protocols outlined using either ultrasound hyperthermia or microwave hyperthermia alone or in combination with radiotherapy. If the results of this project suggest a useful role of hyperthermia in controlling or eradicating spontaneous brain tumors in animals at temperatures which are biologically feasible, then a treatment system and plan will be formulated for treating malignant gliomas in man.